Bistable photoconductive switches particularly suited for frequency-agile, radio-frequency sources

Abstract

A photoconductive switching device is disclosed that has an enhanced speed of response so that its closed (low) and open (high) resistive states are obtained in response to optical illumination in the less than nanosecond regime. The enhanced speed of response is achieved by neutron irradiation of a material preferably comprising GaAs:Si:Cu. An application of the improved photoconductive switching devices is disclosed which allows the realization of a high-power, frequency-agile RF source topology.

What we claim is: 
     
       1. A pulse-switch-out generator comprising: (a) a first photoconductive switching device having on and off high electrical resistance states and comprising a GaAs:Si:Cu material, wherein said Cu has a deep acceptor level Cu B  in said GaAs at an energy level of about 0.44 eV above a valence band of said device and a Fermi level which is above the deep acceptor level Cu B , said first photoconductive switching device having operatively connected electrical contact gaps at respective opposite ends thereof and an exposed region located between said electrical-contact gaps arranged to receive light, one of said contacts arranged to receive an input signal and the other of said contacts arranged to provide an output signal from said first photoconductive switching device;   (b) a second photoconductive switching device having on and off high electrical resistance states and comprising a GaAs:Si:Cu material, wherein said Cu has a deep acceptor level Cu B  in said GaAs at an energy level of about 0.44 eV above a valence band of said device and a Fermi level which is above the deep acceptor level Cu B , said second photoconductive switching device having operatively connected electrical contact gaps at respective opposite ends thereof and an exposed region located between said electrical-contact gaps and arranged to receive light, one of said contacts arranged to receive an input signal and the other of said contacts arranged to provide an output signal from said second photoconductive switching device;   (c) first means for connecting said input contact of said first photoconductive switching device to a relatively high positive potential;   (d) second means for connecting said input contact of said second photoconductive switching device to a relatively high negative potential;   (e) third means for connecting together each of said output contacts of both of said first and second photoconductive switching devices; and   (f) means for directing first and second light pulses having different operating wavelengths onto each of said exposed region of each of said first and second photoconductive switching devices so that each of said first and second photoconductive switching devices transitions from its off-on and on-off electrical resistance states respectively in response to said first and second light pulses.   
     
     
       2. The pulse-switch-out generator according to claim 1, wherein each of said first and second photoconductive switches has recombination centers formed by neutron irradiation and having a density within a predetermined range. 
     
     
       3. The pulse-switch-out generator according to claim 1, wherein said high positive and high negative potentials can be as high as on the order of about 20 kV. 
     
     
       4. The pulse-switch-out generator according to claim 1, wherein said first and second light pulses comprise coherent light having operating wavelengths, with the second wavelength being longer than the first wavelength.